Such loading arms have been known and have been used in many areas of technology. They are usually equipped with a main shaft provided with a gripping device -- the main shaft can be moved in the longitudinal direction by a pneumatic or hydraulic drive. Such main shaft or rod is prevented from rotation by a second rod which runs parallel to the main shaft and is in the form of a guide rod, or by means of a polygonal piece, which can be, for example, a triangular piece.
The known loading arms possess a number of considerable disadvantages. Despite the fact that they are equipped with a main shaft and a guide rod and even if they are constructed with an angular main rod, their accuracy in the end positions, that is, at the transfer position, is directly dependent from the accuracy of their bearings, and thereby from the play thereof. As a result of a lengthy operation in a contaminated environment, the known loading arms become exposed to a great deal of soiling. For this reason, in order to assure an easy motion and operation of the loading arm, their bearings are constructed with a relatively large play which then will result in an inaccurate positioning in the end positions and in the transfer positions.
A further disadvantage of the known loading arm is associated with the sealing of their moveable parts against soiling.
Loading arms having a main shaft and a guiding rod parallel to it must be equipped with a pair of sealing elements with a definite distance between them, while in the case of an angular guide rod, the sealing of the angular edges prevents considerable difficulties. Such sealing problems require a relatively large play in the guide elements of the loading arms if a reliable functioning is the prime requirement.